Concrete Mix Calculator

Calculate how many bags of cement, wheelbarrows of sand, and gravel you need. Common African construction mix ratios included.

Mix RatiosCement BagsWheelbarrows
Project Details
Materials Needed
🧱
Cement
--
--
🏖️
Sand
--
--
🪨
Aggregate/Gravel
--
--
Wet Volume
--
Water (approx)
--

How to Calculate Concrete Materials

Whether you're casting a floor slab in Lagos, building a column in Nairobi, or laying blocks in Accra, getting the right quantities of cement, sand, and aggregate saves money and ensures structural integrity. This calculator uses standard volumetric ratios used across African construction to determine exact quantities.

Understanding Mix Ratios

A mix ratio of 1:2:4 means 1 part cement, 2 parts sand, and 4 parts aggregate by volume. The total parts are 7, so cement constitutes 1/7th of the dry volume. Since dry materials compact when mixed with water, we apply a bulking factor of 1.54 (the dry volume is about 54% more than the wet/final volume) to calculate actual materials needed.

Key Measurements

Frequently Asked Questions

How many bags of cement for a 1:2:4 slab?
For a 1:2:4 mix, you need approximately 6.5 bags of 50kg cement per cubic metre of concrete. A typical room slab of 6m x 4m x 0.15m (3.6 m³) needs about 24 bags of cement, with 10% wastage factored in.
What's the difference between 1:2:4 and 1:3:6?
1:2:4 is stronger (about 20 N/mm²) and used for structural elements like slabs, beams, and foundations. 1:3:6 is weaker (about 10 N/mm²) and used for non-structural work like blinding, lean concrete, and mass fills. Using 1:3:6 for structural work is dangerous.
How many wheelbarrows of sand per bag of cement?
For a 1:2:4 mix, you need approximately 2 headpans (or about 1 wheelbarrow) of sand per bag of cement. For block-laying (1:4), you need about 2 wheelbarrows of sand per bag.